Materials for Solid State Lighting and Displays

Adrian Kitai is Professor in Materials Science and Engineering at McMaster University, Canada.

List of Contributors xi Series Preface xiii

Preface xv

Acknowledgments xvii

About the Editor xix

1. Principles of Solid State Luminescence 1
Adrian Kitai

1.1 Introduction to Radiation from an Accelerating Charge 1

1.2 Radiation from an Oscillating Dipole 4

1.3 Quantum Description of an Electron during a Radiation Event 5

1.4 The Exciton 7

1.5 Two-Electron Atoms 10

1.6 Molecular Excitons 16

1.7 Band-to-Band Transitions 19

1.8 Photometric Units 23

1.9 The Light Emitting Diode 28

References 30

2. Quantum Dots for Displays and Solid State Lighting 31
Jesse R. Manders, Debasis Bera, Lei Qian and Paul H. Holloway

2.1 Introduction 31

2.2 Nanostructured Materials 34

2.3 Quantum Dots 35

2.3.1 History of Quantum Dots 36

2.3.2 Structure and Properties Relationship 36

2.3.3 Quantum Confinement Effects on Band Gap 38

2.4 Relaxation Process of Excitons 41

2.4.1 Radiative Relaxation 42

2.4.2 Nonradiative Relaxation Process 45

2.5 Blinking Effect 46

2.6 Surface Passivation 47

2.6.1 Organically Capped QDs 47

2.6.2 Inorganically Passivated QDs 48

2.7 Synthesis Processes 49

2.7.1 Top-Down Synthesis 49

2.7.2 Bottom-Up Approach 50

2.8 Optical Properties and Applications 53

2.8.1 Displays 53

2.8.2 Solid State Lighting 73

2.8.3 Biological Applications 78

2.9 Perspective 81

Acknowledgments 82

References 82

3. Color Conversion Phosphors for Light Emitting Diodes 91
Jack Silver, George R. Fern and Robert Withnall

3.1 Introduction 91

3.2 Disadvantages of Using LEDs Without Color Conversion Phosphors 93

3.3 Phosphors for Converting the Color of Light Emitted by LEDs 95

3.3.1 General Considerations 95

3.3.2 Requirements of Color Conversion Phosphors 95

3.3.3 Commonly Used Activators in Color Conversion Phosphors 97

3.3.4 Strategies for Generating White Light from LEDs 97

3.3.5 Outstanding Problems with Color Conversion Phosphors for LEDs 98

3.4 Survey of the Synthesis and Properties of Some Currently Available Color Conversion Phosphors 99

3.4.1 Phosphor synthesis 99

3.4.2 Metal Oxide Based Phosphors 99

3.4.3 Metal Sulfide Based Phosphors 113

3.4.4 Metal Nitrides 117

3.4.5 Alkaline Earth Metal Oxo-Nitrides 120

3.4.6 Metal Fluoride Phosphors 121

3.5 Multi-Phosphor pcLEDs 122

3.6 Quantum Dots 123

3.7 Laser Diodes 124

3.8 Conclusions 125

Acknowledgments 125

References 126

4. Nitride and Oxynitride Phosphors for Light Emitting Diodes 135
Le Wang and Rong-Jun Xie

4.1 Introduction 135

4.2 Synthesis of Nitride and Oxynitride Phosphors 138

4.2.1 Solid State Reaction Method 138

4.2.2 Gas Reduction and Nitridation 139

4.2.3 Carbothermal Reduction and Nitridation 140

4.2.4 Alloy Nitridation 140

4.2.5 Ammonothermal Synthesis 141

4.3 Photoluminescence Properties of Nitride and Oxynitride Phosphors 142

4.3.1 Luminescence Spectra of Typical Activators 142

4.4 Emerging Nitride Phosphors and Their Synthesis 165

4.4.1 Narrow-Band Red Nitride Phosphors 165

4.4.2 Narrow-Band Green Nitride Phosphors 167

4.5 Applications of Nitride Phosphors 169

4.5.1 General Lighting 169

4.5.2 LCD Backlight 172

References 173

5. Organic Light Emitting Device Materials for Displays 183
Tyler Davidson-Hall, Yoshitaka Kajiyama and Hany Aziz

5.1 Introduction to OLEDs and Organic Electroluminscent Materials 184

5.2 OLED Light Emitting Materials 186

5.2.1 Neat Emitters 187

5.2.2 Guest Emitters 192

5.2.3 Aggregate-Induced Emission 201

5.3 OLED Displays 203

5.3.1 RGB Color Patterning Approaches 203

5.3.2 Display Addressing Approaches 204

5.3.3 FMM Technology 207

5.3.4 Alternative Fabrication Techniques 208

5.3.5 Outlook on OLED Display Commercialization 212

5.4 Quantum Dot Light Emitting Devices 213

5.4.1 QD Optimization by Core–Shell Morphology 214

5.4.2 Organic Charge Transport QD-LEDs 215

5.4.3 Hybrid Organic–Inorganic Charge Transport QD-LEDs 217

5.4.4 Energy Transfer Enhanced QD-LEDs 219

5.4.5 QD-LED Lifetime 220

References 220

6. White-Light Emitting Materials for Organic Light-Emitting Diode-Based Displays and Lighting 231
Simone Lenk, Michael Thomschke and Sebastian Reineke

6.1 Introduction 231

6.2 White Organic Light-Emitting Diodes 233

6.3 Photometry and Radiometry 236

6.3.1 OLED Efficiencies 239

6.3.2 Color Stimulus Specification 239

6.3.3 Color Correlated Temperature 240

6.3.4 Color Rendering Index 241

6.3.5 White Light 241

6.4 Device Optics 242

6.4.1 Optical Properties of Thin Films 242

6.4.2 Optical Outcoupling 245

6.4.3 Top-Emitting OLEDs 247

6.4.4 Simulation Tools 248

6.5 Materials for Efficient White Electroluminescence 248

6.5.1 Spin Statistics for Electroluminescence 248

6.5.2 Fluorescence-Emitting Molecules 249

6.5.3 Advanced Concepts Comprising Fluorescent Emitters 251

6.5.4 Phosphorescence-Emitting Molecules 251

6.5.5 Single White-Light Emitting Phosphorescent Materials 256

6.5.6 Thermally Activated Delayed Fluorescence-Based Emitters 257

6.5.7 Phosphorescence Versus Thermally Activated Delayed Fluorescence 261

6.5.8 TADF Assisted Fluorescence (TAF) Emitters 263

6.6 Polymer Concepts 263

6.6.1 Various Concepts Involving Polymer Materials 265

6.6.2 Learning from High Performance Small Molecules for High Efficiency Polymers 267

6.7 Summary and Outlook 268

References 269

7. Light Emitting Diode Materials and Devices 273
Michael R. Krames

7.1 Introduction 273

7.2 Light Emitting Diode Basics 273

7.2.1 Construction 273

7.2.2 Recombination Processes 275

7.2.3 Heterojunctions 277

7.2.4 Quantum Wells 278

7.2.5 Current Injection 278

7.2.6 Forward voltage 280

7.3 Material Systems 280

7.3.1 Ga(As,P) 280

7.3.2 Ga(As,P):N 281

7.3.3 (Al,Ga)As 282

7.3.4 (Al,Ga)InP 282

7.3.5 (Ga,In)N 283

7.3.6 White Light Generation 285

7.4 Packaging Technologies 288

7.4.1 Low Power 288

7.4.2 Mid Power 288

7.4.3 High Power 289

7.4.4 Chip-On-Board LEDs 290

7.4.5 Multi-Color LEDs 290

7.4.6 Electrostatic Discharge Protection 290

7.5 Performance 291

7.5.1 Light Extraction Efficiency 291

7.5.2 Monochromatic Performance 292

7.5.3 White-Emitting Performance 298

7.5.4 Temperature Effects 306

7.5.5 Reliability 306

References 307

8. Alternating Current Thin Film and Powder Electroluminescence 313
Adrian Kitai

8.1 Introduction 313

8.2 Background of TFEL 314

8.2.1 Thick Film Dielectric EL Structure 315

8.2.2 Ceramic Sheet Dielectric EL 316

8.2.3 Sphere-Supported TFEL 316

8.3 Theory of Operation 317

8.4 Electroluminescent Phosphors 324

8.5 Thin Film Double-Insulating EL Devices 325

8.6 Current Status of TFEL 327

8.7 Background of AC Powder EL 328

8.8 Mechanism of Light Emission in AC Powder EL 329

8.9 Electroluminescence Characteristics of AC Powder EL Materials 333

8.10 Emission Spectra of AC Powder EL 334

8.11 Luminance Degradation 335

8.12 Moisture and Operating Environment 336

8.13 Current Status and Limitations of Powder EL 336

8.14 Research Directions in AC Powder EL and TFEL 336

References 337

Index 339